Retarder control systems



Jan. 9, 1968 E. R. KNAUER ETAL 3,363,095

RETARDER CONTROL SYSTEMS Filed March 2, 1964 3 Sheets-Sheet l SPEED RETARDER ACTUATOR 5 I I RETARDER ACTUATOR T r-' SPEED SPEED $PEED 33 CONTROL- CONTROL CONTRQL I NVENTOR S BPW/N R. KNAUER ROBERT B. M0 CU/VE Jan. 9,1968 E. R. KNAUER ETAL 3,363,095

RETARDER CONTROL SYSTEMS Filed March 2, 1964 5 Sheets-Sheet 2 INVENTOKS ERW/IV R KNAUER ROBERT Q Ma cu/vs R p H H United States Patent 3,363,095 RETARDER CONTROL SYSTEMS Erwin R. Knauer, Woodclilf Lake, and Robert B. McC'une,

Allendale, N.J., assignors to Abex Corporation, a corporalion of Delaware Filed Mar. 2, 1964, Ser. No. 348,734 Claims. (Cl. 246182) This invention relates to a new and improved apparatus for braking railroad cars in the operation of a railroad classification yard or the like. More particularly, the invention relates to a new and improved speed-sensitive control system for a railway car retarder.

In the operation of a railroad classification yard, railroad cars are ordinarily released at the top of an incline or hump and roll down the incline and into the branching classification tracks of the yard. It is usually necessary to brake the cars at one or more points along the gang or feeder track and it may also be necessary to provide additional braking along the classification tracks of the yard. The track brakes or car retarders used for this purpose ordinarily comprise pairs of elongated rail-like brake shoes that engage the sides of the car wheels. Car retarders of this kind are necessary to prevent coupling at excessive speeds, in the use of the classification yard, with resultant damage to the railroad cars and their contents.

Relatively elaborate control systems have been utilized for centralized control of all of the car retarders in a classification yard. These control systems have frequently utilized radar or other costly speed-sensing devices, together with car weighing apparatus and other mechanisms for determining various factors that afiect the rollability of individual cars. Control systems of this kind, however, are not usually suitable for use with individual track brakes located at the classification tracks of the yard, since there are usually many such classification tracks and the cost would be prohibitive. By the same token, radar speed control and similar arrangements are not economically feasible in relatively small yards.

It is a principal object of the present invention, therefore, to provide a new and improved speed-sensitive control system for a railway vehicle retarder that is relatively simple and inexpensive in construction yet highly dependable in operation.

Another object of the invention is to provide a new and improved multiple-level retarder control system that adjusts the braking effect of a railway car retarder in accordance with the instantaneous speed of a railway vehicle moving through the retarder.

An additional object of the invention is to provide a new and improved speed-sensitive control system in which the movement of a railway car along the track may be sensed periodically, by switches actuated by the car wheels or by similar conventional sensing devices, yet which utilizes only a minimum of speed-determination apparatus.

A further object of the invention is to provide a new and improved speed-sensitive control system for a railway vehicle retarder which is efiective to handle a single car or a multiple cut of cars, yet which operates directly from the wheels of the cars, as they traverse a railway car retarder, without confusion.

A specific object of the invention is to protect a speedsensitive control system, in which the movement of a railway car is sensed directly by contact with the car wheels, against erroneous operation resulting from a stoppage of the car in contact with One or more speed sensing devices.

Another object of the invention is to provide a new and improved speed-sensitive control system, for a railway vehicle retarder, in which the principal speed determination or timing means comprises one or more timing relays interlocked to maintain the retarder in a released condition when the vehicle traversing the retarder has been reduced in speed below a predetermined critical level.

An additional object of the invention is to provide for wide-range accurately controlled time adjustment in a single-relay timing circuit controlling a railway car retarder. 5a

Another object of the invention is to provide an im proved speed-sensitive retarder control system readily grdaptable to multiple-speed and multiple-section operaron.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what 1s now considered to be the best mode contemplated for applying these principles. Other embodiments of the inventron embodying the same or equivalent principles may. be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

FIG. 1 is a partially schematic plan view of a railway car retarder that may be actuated and controlled in accordance with the present invention;

FIG. 2 is a schematic diagram of a control system constructed in accordance with one embodiment of the present invention;

FIG. 3 is a simplified elevation view of typical railway cars, used to explain certain important relationships between the car dimensions and the construction of the control system of the invention;

FIG. 4 is a block diagram of a multi-section retarder control system constructed in accordance with a second embodiment of the invention; and

FIG. 5 is a circuit diagram of the system of FIG. 4.

FIG. 1 illustrates a substantially conventional railway car retarder 19 in which the control system of the present invention may be incorporated. Car retarder 10 includes a relatively short section of track comprising the traffic rails 11 and 12. The railway track in which rail sections 11 and 12 are incorporated is preferably inclined to permit cars to roll through retarder 1G in the direction indicated by the arrow A. A pair of car retarding rails or brake shoes 13, referred to hereinafter as retarder elements, are disposed immediately adjacent rail 11 in positron to engage the opposite sides of a car wheel as the wheel traverses track section 11. A similar pair of re-' tarder rails or elements 14 are disposed adjacent trafiic rail 12. Suitable means are provided for actuating retarder rails 13 and 14 between braking and released positrons, this retarding operating means being generally indicated in FIG. 1 as the retarder actuator 15. Retarder actuator 15 may comprise any suitable electrical, mechanical, pneumatic or hydraulic mechanism capable of moving retarder rails 13 and 14 between an open or released condition and a closed or retarding condition. Regardless of the basic drive incorporated in the retarding operating means, however, this apparatus should be constructed for electrical actuation. Moreover, in the preferred embodiments described in connection with FIGS. 3 and 4, retarder actuator 15 should be capable of providin three distinct levels of retarding or braking pressure, as explained more fully hereinafter.

In order to provide for braking of railroad cars in retarder 19, according to the present invention, it is necessary to sense the movement of a railroad car or cars along track sections 11 and 12. The means provided for this purpose comprises a series of sensing devices 21, 22, 23, 24, 25 and 26 located at predetermined spaced position along trafiic rail '11. Each of the devices 21-26 may comprise a switch of substantially conventional construction that is actuated from an open condition to a closed condition, or vice versa, by engagement with the flange of a railway vehicle wheel moving along trafi'ic rail 11. There is no critical number of sensing switches or other sensing devices; a relatively large number may be utilized or the sensing devices may be quite limited in number. The individual sensing devices are electrically connected to a speed control circuit 39 which, in turn, is connected to retarder actuator 15. The initial embodiment of the present invention comprises sensing devices 21-26 and control circuit 30, shown in detail in FIG. 2.

Control circuit 30, as shown in FIG. 2, comprises a pair of power supply lines or buses 28 or 29 connected to the positive and negative terminals, respectively, of a suitable DC power supply (not shown). Each of the sensing devices 2125 comprises a double-pole double-throw switch with. one side of the switch connected, in each instance, to the positive bus 28, as described more fully hereinafter. These sensing devices each include a capacitor circuit for developing a pulse output signal, as set forth in detail subsequently. The last sensing device in the series, sensing device 26, is a single-pole single-throw switch having one terminal connected to the positive supply line.

The control circuit further includes a series of connecting or interlocking relays 3135. Relay 31 is actuated by sensing device 21, by means of an auxiliary relay 262 as set forth hereinafter. Relays 32 through 35 are individually connected to and are energized by sensing switches 22 through 25 respectively. The other relay in the series, relay 36, is a reset relay, actuated by switch 26, that is used to re-establish initial operating conditions for control circuit 30 upon completion of a .full cycle of operation.

Relay 32 comprises two sets of normally closed contacts 41 and 42 and three sets of normally open contacts 43, 44 and 45, all controlled by an operating coil 46. The next relay in the series, relay 33, comprises the operating coil 55, one pair of normally closed contacts 51, and three sets of normally open contacts 5254. Subsequent relays in the series are similar; thus, relay 34 includes coil 65, a pair of normally closed contacts 61, and three normally open contact pairs 62-64, and relay 35 includes the normally closed contacts 71, the normally open contacts 72-74, and the coil 75. The last relay in the series, reset relay 36, is somewhat different, afiording three sets of normally closed contacts 81, 82 and 83. and one pair of normally open contacts 84 actuated by an operating coil 85. The initial relay 31, on the other hand, utilizes only two sets of normally open contacts 91 and 92 controlled by the operating coil 93.

A principal operating component of control circuit 30 is a signal-operated timing means generally indicated by the reference numeral 100. Timing means 109 comprises three slow-release tirnin relays 101, 192 and 163. Therelay 101 includes two sets of normally open contacts 111 and 112 and an operating coil 113. Relay 102 is quite similar and comprises two normally open contact pairs 115 and 116 and an operating coil 117. The third timing relay, relay 103, utilizes only one set of normally open contacts 118 actuated by an operating coil 119.

Each of the three timing relays 1131-103 has associated therewith an output or control relay. the control relays being the devices 121, 122 and 123. Each of the control relays is provided with two sets of normally open contacts. Thus, the first control relay, relay 121, includes the normally open contacts 131 and 132 controlled by an operating coil 133. Relay 122 comprises the operating coil 134 and the normally open contacts 135 and 136. Relay 123 includes the normally open contacts 137 and 138 actuated by an operating coil 139.

Each of sensing devices 21-25 comprises a double-pole double-throw switch positioned to be actuated by the flange of 'a railway car wheel. Thus, switch 21 comprises a first movable contact 231 that is normally engaged with a fixed contact 232 butwhich engages a second fixed contact 233 when the switch is actuated. The other pole of switch 21 comprises a movable contact 235 normally engaged with a fixed contact 236 but engageable with a second fixed contact 237 upon actuation of the switch. Contacts 232 and 236 are connected directly to the positive bus 28. Movable contact 231 is connected to the negative bus through the series combination of a resistor 238 and a capacitor 239. Similarly, movable contact 235 is connected to the negative bus through a resistor 241 in series with a capacitor 242. The contacts 233 and 237 are connected to the interlocking and connecting circuit of the system. Thus, contact 233 is connected to the normally closed contacts 41 of relay 32 and contact 237 of the sensing switch is connected to relay contacts 42.

The arrangement for switch 22 is similar but specifically different. Switch 22 comprises a first movable contact 251 normally engaged with a fixed contact 252 but actuatable to engage a second fixed contact 253. The other pole of the switch comprises a movable contact 255 ordinarily engaged with a fixed contact 256 but engageable with a further fixed contact 257 upon actuation of the switch. In the upper half of switch 22, movable contact 251 is connected directly to the positive bus 28.

' Fixed contact 252 is left open-circuited and fixed contact 253 is connected to the normally open contacts 92 in the initial interlocking relay 31. In the lower half of switch 22, fixed contact 256 is connected to the positive bus and contact 257 is connected to contacts 51 of relay 33. Movable contact 256 is returned to the negative bus through the series combination of a resistor 258 and a capacitor 259. i

The construction and wiring arrangement used for sensing devices 23-25 is the same as for sensing switch 22 and, accordingly, need not be described in detail.

The circuit arrangement of FIG. 2 also includes two auxiliary relays 261 and 262. Relay 261 is provided with a pair of normally open contacts 263 connected between the negative bus 29 and the operating coil 113 of the initial timing relay, device 101. The operating coil 264 of relay '261 has one terminal connected to the negative bus and the other terminal connected to normally closed contacts 41 in relay 32 and to normally open contacts 44, 53, 63 and 73 in relays 32, 33, 34 and 35 respectively. Auxiliary rel-ay 261 is interposed in the circuit utilized to apply initiating signals from the sensing switches to timing means 100 and'specificallyto the initial ingly, the second auxiliary relay 262 controls energiza-' tion of the control relays of the system. The operating coil 275 of relay 262 is connected to contacts 42 of inter locking relay 32 and to the negative bus 29.

One terminal of each of the interlocking relay operating coils 46, 55, 65, and 93 is connected to a con- I ductor 94 and, through the normally closed "contacts 82 and 83 of relay 36, to negative bus 29. The other terminal of operating coil 93 in interlock relay 31, as noted above, is connected to the cont-acts 274 of relay 262. Relay 31 is also provided with a holding circuit extending from its operating coil 93 through its normally open contacts 91 to the positive bus 28.

The energizing circuit for coil 46 of relay 32 includes the normally open contacts 92 of interlockrelay 31 and one contact 253 of sensing switch 22. A holding circuit is provided for the relay, in this instance by a connection to the positive bus through the normally open cont acts 43 of the relay. Operating coil 55 of relay 33 is connected back to the positive bus through the normally open contacts 45 of the preceding relay 32 and thence to the positive bus through sensing switch 23. Again, a holding circuit is provided, in this instance through the normally open contacts 52. Similar circuits are afiorded in each of the next two relays. Coil 65 of relay 34 is connected to the positive supply through normally open contacts 54 cf the preceding relay 33 and through sensing switch 24, with a parallel holding circuit through its normally open contacts 62. Coil 75 of relay 35 is connected to sensing switch 25 through the normally open contacts 64 of the preceding relay, with a holding circuit established through contacts 72.

The connection arrangement for relay 36 is somewhat difierent. Operating coil 85 has one terminal connected to the positive bus through sensing switch 26 in a circuit that includes, in series, the normally open contact 74 of the preceding relay. This circuit is paralleled by a holding circuit that includes, in series, the normally open contacts 84 of the relay. The other terminal of coil 85 is returned directly to the negative bus 29.

The contact 233 of the initial sensing device, switch 21, is connected through the normally closed contacts 41 of relay 32 to the coil 264 of relay 261 to control actuation of the initial slow-release timing relay 101 by closing contacts 263 and connecting coil 113 to the positive bus. The other terminal of coil 113 is returned directly to negative bus 29. Relays 101, 102 and 103 are connected for sequential operation. Thus, one terminal of the operating coil 117 for relay 102 is connected directly to negative bus 29 and the other terminal of this coil is connected to positive bus 28 through the normally open contacts 111 of relay 101. Coil 119 of relay 103, on the other hand, is connected to the positive bus through the normally open contacts 115 of the second timing relay 102, being provided with a direct connection to the negative bus.

Contact 237 of switch 21 is connected through the normally closed contacts 42 of connecting relay 32 to the relay 262 to control energization of each of the operating coils 133, 134 and 139 of control relays 121, 122 and 123. Each of coils 133, 134 and 139 is connected to the positive bus through the normally open contacts of relay 262 and is returned directly to the negative bus 29. Each of the control relays is also provided with a holding circuit. The holding circuit for relay 121 extends from operating coil 133 through its normally open relay contacts 131 and through the normally open contacts 112 of timing relay 101 to the positive bus 28. The holding circuit for control relay 122 is similar and includes the normally open contacts 135 of the control relay, connected in series with contacts 116 of relay 102. The holding circuit for relay 123 comprises its contacts 137 and the normally open contacts 118 of timing relay 103.

As noted hereinabove, relays 101-103 are slow-release timing devices. Thus, a capacitor 141 and a resistor 142 are connected in series with each other and in parallel with operating coil 113 of relay 101. An adjustable resistor 143 is connected in parallel with capacitor 141. Similar time delay circuits are connected in parallel with operating coils 117 and 119 of relays 102 and 103, respectively. Thus, the delay circuit for relay 102 comprises the capacitor 144 and the delay circuit for relay 103 includes the storage capacitor 145.

In considering operation of car retarder and the associated speed-sensitive control system, it may be assumed that a railway vehicle such as the car 150 (FIG. 3) enters the retarder in the direction indicated by the arrows A (FIGS. l-3). As the car moves along traflic rail 11, the leading wheel 151 of the car first engages and closes switch 21, the initial sensing device of the control system.

When the sensing switch is engaged by the car wheel, contact 231 closes on contact 233 and the positive charge on capacitor 239 is discharged through contacts 41 of relay 32 and through the operating coil of auxiliary relay261. The auxiliary relay is operated momentarily, closing con- 6 tacts 263 and supplying a short-duration initiating signal to operating coil 113 of the initial timing device, relay 101. Resistor 238 serves to suppress arcing in the circuit.

Similarly, actuation of switch 21 closes its second movable contact 235 on contact 237 and discharges capacitor 242 through contacts 42 of relay 32 and through coil 275 of auxiliary relay 262. Thus, the second auxiliary relay 262 is also operated for a short time interval, closing contacts 271-274. The closing of contacts 271-273 supplies an initiating signal to the three control relays 121-123. The closing of contacts 274 supplies an energizing signal to interlocking relay 31.

The auxiliary relays remain energized only for a short time interval, determined by the discharge time for capacitors 239 and 242. Consequently, even it a car wheel holds switch 21 in its actuated condition indefinitely, relays 261 and 262 will release when capacitors 239 and 242 are discharged. This enables timing means to time out and prevents the retarder from being maintained in maximum braking condition indefinitely. Thus, the retarder is released to its normal or open condition and the car is permitted to roll out of the retarder.

The same arrangement is followed with respect to the initiating-signal sections of subsequent sensing switches 22-25. Thus, closing of contacts 255 and 257 in switch 22 supplies a short-duration initiating signal to auxiliary relay 261 through the circuit comprising contacts 51 and contacts 44. Again, the auxiliary relay is energized only for the time required to discharge capacitor 259. It is not necessary to utilize a similar arrangement with respect to contacts 251 and 253, since the retarder would not be held in operation indefinitely in response to continued closure of these contacts. As noted above, actuation of auxiliary relay 262 energizes relay 31 in a circuit extending from the positive bus through contacts 274 to operating coil 93 and then from auxiliary bus 94 through the normally closed contacts 82 and 83 of relay 36 to the negative bus 29. Energization of relay 31 closes its contacts 91 and 92. The closing of contacts 91 establishes a holding circuit for the relay, so that the relay remains in energized condition even though the sensing switch is closed only momentarily. Closing of contacts 92 sets up an energizing circuit for the next relay in the series, relay 32.

Actuation of relay 261 upon closing of sensing switch 21 by the vehicle Wheel, as noted above, energizes the first timing device, timing relay 101. Consequently, contacts 111 are closed, energizing the second timing device, relay 102. This closes contacts 115 and, in turn, energizes the third timing relay 103. Of course, the lower contacts on each of the relays 101, 102 and 103 are also closed, these being contacts 112, 116 and 118.

Actuation of sensing switch 21 by the leading wheel of the railway vehicle, and the consequent energization of relay 262, also energizes the operating coils of each of control relays 121, 122 and 123. As soon as coils 133, 134 and 139 are energized, contacts 131, 135 and 137 are closed. This establishes a holding circuit for each of the control relays, the holding circuit in each instance including one set of contacts in the associated timing relay. For example, the holding circuit for control relay 121 extends through its contacts 131 and through contacts 112 of timing relay 101 to the positive bus 28. Actuation of the three control relays also closes their remaining contacts 132, 136 and 138, completing three operating circuits for the retarder actuator 15 (FIG. 1). In the following discussion, it should be understood that maximum retarding effort is applied, in retarder 10, when all three of the control relays are energized and all three of contacts 132, 136 and 138 are closed. Lower braking conditions are established if only contacts 136 and 138 are closed or when only contacts 138 are closed.

Relay 101 is energized directly for only a short interval, the time required for the discharge of capacitor 239. The relay remains in its actuated condition for a predetermined time interval, however, due to the slow-release characteristics afforded by the RC circuit 141-143 connected in parallel with operating coil 113 of the relay. That is, capacitor 141 is charged upon the initial closing of switch 21 and the relay remains in its actuated or closed condition until the capacitor discharges. The same condition applies to timing devices 102 and 103. The time delays for relays 101, 102 and 103 are established in accordance with the braking conditions desired for difierent speed levels. The individualtime delays for relays 101-103 may be equal or they may be different from each other, as explained more fully hereinafter.

Continued movement of the railway vehicle along traffic rail 11, in the direction of arrow A, causes the lead wheel of the vehicle to engage and close the second sensing device, switch 22. Initially, it may be assumed that the railway car is moving fast enough to close switch 22 before any of the three slow-release relays 101-103 drops out. Closing of switch 22 energizes operating coil 46 of connecting relay 32 through a path comprising, in series, the positive bus 28, contacts 251 and 253 of switch 22, contacts 92 of relay 31, and the operating coil, the connection to the negative bus again extending through bus 94 and contacts 82 and 83 of relay 36. It will be recalled that contacts 92 have previously been closed upon energization of relay 31 and that this relay remains energized through its holding circuit, comprising contacts 91. As soon as relay 32 is energized, contacts 43 are closed, establishing a holding circuit for this relay.

Actuation of relay 32 opens contacts 41 and 42 to prevent subsequent actuation of timing relays 101-103 or control relays 121-123 through sensing switch 21. Consequently, if the distance D between sensing switches 21 and 22 is made smaller than the wheelbase W of railway vehicle 150 (see FIG. 3) the second wheel of the railway car cannot re-initiate operation of the control system. In this manner, relay 32 operates to prevent erroneous operation of the system and to restrict initial control to the lead Wheel of the railway car. Closing of contacts 45 of relay 32, on the other hand, establishes an energizing circuit for the next relay in the sequence, relay 33.

Contacts 44 of relay 32 are also closed upon energization of the relay. Closing of these contacts completes an initiating signal circuit to the first auxiliary relay 261. This circuit, starting at the negative bus 29, extends through capacitor 259, resistor 258, contacts 255, 257 of switch 22, through contacts 51 of relay 33, through nowclosed contacts 44, and through operating coil 264 to the positive bus. Accordingly, contacts 263 close and relay 101 is again momentarily energized. As a result, this relay cannot drop out until a second time interval determined by the delay circuit 141143 has passed. Of course, the other timing relays 102 and 103 remain in energized condition since their connections are dependent upon the energization state of relay 101.

Continued movement of the railway car along trafiic rail 11 causes the lead wheel of the car to engage, in succession, the remaining sensing devices 23, 24 and 25. When sensing switch 23 is closed, it is effective to energize relay 33 through a circuit comprising the sensing switch, contacts 45 of relay 32 (these have previously been closed), operating coil 55 and auxiliary bus 94. Energization of relay 33 opens contacts 51, so that subsequent closing of switch 22 cannot actuate relay 261 to supply an initiating signal to the timing relays. However, relay 261 is momentarily energized and an initiating signal is supplied to the timing relays from the switch 23, the auxiliary relay being energized through contacts 53 of relay 33 and normally closed contacts 61 of relay 34 at the time the car wheel engages and closes sensing switch 23. Actuation of the next sensing switch, device 24, again supplies an initiating signal to the timing relay 101, through auxiliary relay 261, and at the same time efiectively opens the operating circuit from the preceding sensing switch 23 to prevent false triggering of'the timing relay by the second wheel of the car.

As the car leaves the retarder, the lead wheel engages and closes the final sensing device, the reset switch 26. Closing of this switch establishes an operating circuit from the positive bus 28 through the switch and through contacts 74 of the preceding relay, which has previously been energized, and through operating coil to the negative bus 29. Energization of the relay establishes a holding circuit through its contacts 84 that is effective to keep the relay energized as long as switch 26 is closed. This is necessary because actuation of relay 36 opens contacts 82 and 83, causing relay 35 to drop out and opening contacts 74 in the original energizing circuit for relay 36. Opening of'contacts 82 and 83 also effectively assures de-energization of all of the preceding relays 31-35 to re-establish the initial operating conditions for the system. Contacts 81 open as soon as relay 36 is energized, to protect against erroneous energization of auxiliary relay 261.

The foregoing discussion of operation of the sensing switches and their associated connecting and interlocking relays does not take into account the operation of timing devices 101-103 of timing means 100. Consideration of the functioning of timing means may be facilitated by establishing examples of practical time delays and sensing device spacings. Thus, and solely by way of example, the spacing D between the individual sensing devices (FIG. 1) may be established at 3.5 feet, a distance substantially smaller than the accepted standard wheelbase W for railway vehicles. A critical release speed may be taken as four miles per hour, this being a generally acceptable value in some classification yards. Under these circumstances, the total delay time for timing relays 101- 103 is approximately 0.6 second. The time delays may be equal to each other, thus establishing the time delay for each relay at 0.2 second, a practical and easily obtainable value with commercially available slow-release relays.

Using the foregoing exemplary delay values, it may be considered that the railway car enters retarder 10 in they direction of arrow A at a speed in excess of twelve miles per hour. At this speed, the lead wheel of the car traverses the distance D between sensing devices 21 and 22 in less than 0.2 second. Consequently, at the time sensing switch 22 is closed, none of the timing relays 101- 103 have dropped out, since the delay interval for each is 0.2 second. Accordingly, the railway vehicle enters retarder 10 with the retarder actuated to its maximum retarding condition by operating means 15, all of the control relays 121-123 being energized.

As the car is braked by retarder 10, its speed decreases, and the car speed may be reduced below twelve miles per hour before it reaches the second sensing device, switch 23. That is, the initial braking effect of retarder 10, operating with maximum braking force, may slow the car up enough so that it requires more than 0.2. second to traverse the distance between switches 22 and 23. Consequently, timing relay 101 drops out before the car Wheel closes switch 23. When relay 101 is thus effectivelyde-energized, its contacts 111 open, thereby opening the operating circuit to the operating coil of the second timing device, relay 102. However, relay 102 remains energized from the capacitor 144. Contacts 112 also open, however, breaking the holding circuit for control relay 121. Consequently, control relay 121 drops out and one of the actuating circuits to retarder actuator 15 is interrupted. This reduces the braking force applied by retarder 10, establishing the retarder in its second braking condition.

It the car wheel engages and closes sensing switch 23 before 0.4 second has elapsed, relay 101 is again energized momentarily through auxiliary relay 261 and again completes an energizing circuit to relay 102. Consequently, relay 102 does not have time to drop out, having been maintained continuously in energized condition beyond the drop out time for relay 101 by the delay circuit comprising capacitors 144. Control relay 121 is not energized again because there is no connection from switch 23 to the operating coil of the auxiliary relay 262 that actuates this control relay and, accordingly, there is no way to complete an operating circuit for coil 133. Accordingly, and since the same condition applies to the remaining sensing devices in the system, control relay 121 remains de-energized throughout this cycle of operation of the retarder control system.

The car is subjected to further braking in retarder as it traverses the distance between sensing devices 23 and 24 and may be slowed up enough so that the time required to travel this distance exceeds 0.4 second, the sum of the time delays of relays 101 and 102. Accordingly, before the car Wheel reaches sensing switch 24, relay 101 drops out and relay 102 also drops out. As soon as relay 102 drops out, control relay 122 is de-energized by opening of the timing relay contacts 116. Consequently, the second of the three actuating circuits for retarder actuator is interrupted by opening of contacts 136 of control relay 122, establishing the retarder in its third braking condition. That is, only the one actuating circuit through contacts 138 of relay 123 remains closed, limiting retarder operation to the least effective of the three braking conditions. The car may close switch 24 before the third timing device, relay 103, is returned to its initial operating condition. Accordingly, closing of switch 24 is again efiective to actuate relay 261 and energize timing relays 101 and 102 and hence to maintain timing device 103 in continuous operation. As long as this one timing device is maintained continuously in operation, the third braking condition for the relay is also maintained and the car is not released to roll freely through the retarder.

By the time the leading wheel of the railway car reaches sensing switch 25, it may have been slowed enough so that it is moving at or below the critical release speed of four miles per hour. If the average speed is four miles per hour or less as the car wheel moves between devices 24 and 25, the total elapsed time exceeds the combined delay intervals for devices 101, 102 and 103; that is, it exceeds 0.6 second. Under these circumstances, all three of the timing relays drop out before switch 25 is closed. When this happens, the third control relay 123 is deenergized by opening of contacts 118 in timing relay 103. The control relay contacts 128 are opened and the retarder is effectively de-energized. That is, the retarder returns to its normal released condition and the railway car is no longer braked. Subsequent movement of the car causes the lead wheel to actuate the final sensing device, switch 26, which resets the entire circuit for a further cycle of operation as described hereinbefore.

From the foregoing description, it will be apparent that braking of a given car may not require use of all of the retarding conditions of retarder 10. For example, the initial speed determination between the locations of sensing devices 21 and 22 may show that the car is already moving at a speed less than four miles per hour, the critical release speed. On such a slow moving car, all of the timing devices of timing means 100 will drop out before the car reaches sensing device 22, and retarder 10 will be effectively actuated to its released condition without braking the car at all. A car moving at a speed of more than four miles per hour but less than six miles per hour will be subjected only to the lowest braking condition of the retarder. A car traveling at more than six miles per hour but less than twelve miles per hour finds the retarder in its intermediate braking condition, and only cars traveling in excess of twelve miles per hour are subjected to the maximum braking effect from the retarder. Of course, all of these speed values can be varied by adjustment of the time delays of timing relays 101 103. Thus, if the time delays for release of relays 101, 102 and 103 are set at 0.265, 0.135 and 0.2 second, respectively, the critical speeds are 9, 6 and 4 miles per hour. Other values may be selected to meet the classification yard requirements.

If only individual cars are to be braked in retarder 10, the overall length L of the retarder control system (FIG. 1) is not critical, particularly if the application is such that control in accordance with one sensing of car speed is adequate. However, it may be desirable to monitor the speed of the car in accordance with the movement of the leading wheel on the second truck, particularly where the maximum braking eifect available from retarder 10 may be insufiicient to slow some cars below the critical release speed. Moreover, it becomes virtually essential to make more than one speed determination if a multiple cut of cars is to be handled by retarder 10, since the great weight of a number of cars may make it impossible for the retarder to reduce car speed adequately merely by braking the leading car. To provide for multiple monitoring of individual cars, in accordance with both the leading truck and the second truck, and to accommodate multiple cuts of cars, the total length L encompassed by sensing devices 2126 should be made less than the 'frontto-rear spacing S between car trucks (FIG. 3).

Thus, considering a single car 150, the lead wheel 151 of the car (FIG. 3) actuates the control system as described hereinabove. The interlocking and connecting relays 31-36 prevent actuation of the system by the trailing wheel 152 of the first car truck, as described hereinbefore. If length L of the sensing system is less than the inter-truck spacing S of the railway car, wheel 152 clears the final sensing switch 26 before the lead wheel 153 of the second car truck reaches the first sensing device, switch 21. Consequently, the complete speed sending operation is repeated with respect to wheel 153 and retarder 10 is actuated to brake the rear wheels of the railway vehicle if it is still traveling over the critical release speed. Of course, if its speed has already been reduced below the critical release speed, the car traverses the retarder without further braking. Again, the second wheel 154 in the truck does not actuate the speed-sensitive control system due to the interlocking operation of relays 31-36.

By the same token, the leading wheel 155 on the next car in a multiple-car cut would not actuate the speedsensitive control system because the leading wheel 155 would ordinarily engage the initial sensing switch 21 before wheel 154 on the preceding car clears switch 26. That is, the control system would not be reset for a new cycle of operation in time to permit proper control by wheel 155 on the second car or by the succeeding wheel 156 on the same truck. However, with the limitation on length L of the sensing system noted hereinabove, the system is reset in time for a complete cycle of operation responsive to movement of the leading wheel 157, on the second truck of the second car, through the retarder. Thus, if the cars are moving at a speed in excess of the critical speed by the time the lead wheel 157 on the second truck of the second car enters the retarder, the retarder is again automatically actuated to brake the car at a level commensurate with its speed. This holds true with respect to each succeeding car whenever a multiple-car is braked in retarder 10.

The speed-sensitive control system comprising circuit 30 and sensing devices 2126, as described hereinabove, is relatively simple and expensive in construction, the basic components constituting switches and simple relays that are commercially available. By the same token, the system is highly dependable in operation. The system is effective to monitor the speed of a railway car or cars passing through the retarder substantially continuously and adjusts the braking condition of retarder 10 to a level commensurate with the speed of the car being braked. On the other hand, the system requires only a minimum of speed-determination apparatus. Thus, for each critical speed there is just one timing device which is effective to hold the retarder in a given operating condition as long as that device is continuously energized. The control system can be operated in conjunction with individual cars or with multiple-car cuts without change or modification and without confusion in operation resulting from the presence of additional cars.

FIGS. 4 and 5 illustrate another embodiment of the present invention, utilized to control a multiple-section car retarder generally identified by the reference numeral 300. Retarder 300 includes a series of three retarder rails 301, 302 and 303 along the traific rail 11. Preferably, paired retarder rails would be utilized as described in con nection with the single-section retarder of FIG. 1. Along rail 11 there are a series of sensing switches that are employed to derive the basic system data necessary for actuation of the retarder control system. At the left-hand side of retarder 300, the side of the retarder from which cars enter, the initial switch is identified by reference numeral 401. Switch 401 is followed, in sequence, by switches 402 through 411, all of which are connected to a first speed control circuit 330. Speed control circuit 330 is connected to a retarder actuator circuit 315 that actuates the retarder rails 301-303.

Following the last switch 411 in the initial series, there is a further series of sensing switches 412419, all of which are connected to an additional speed control circuit 331. Circuit 331 is also connected to the initial speed control circuit 330 as explained in detail hereinafter. Control circuit 331 is further connected to retarder actuator 315. Circuit 331 is additionally connected to a further speed control device 332 that is also connected to the actuator 315. In addition, speed control device 332 is connected to each sensing switch in a further series comprising switches 420 through 427. All of the switches 401 through 427 are disposed at regularly spaced intervals along trafiic rail 11 and, as in the previously described embodiments, the spacing between individual sensing switches is made smaller than the standard truck wheelbase W for railroad cars.

As shown in the detail circuit diagram of FIG. 5, speed control unit 330 comprises two principal operating circuits 330A and 330B. Circuit 330A includes sensing switches 401-411 and a related series of connecting or interlocking relays 431-441, there being one relay for each switch. Only switches 401403, 410 and 411, and relays 431433, 440, and 441 are shown in the circuit diagram, since the connections for the remaining sensing switches and associated relays are all the same as for the illustrated relays 432 and 433. As before, the power supply comprises a pair of buses 28 and 29.

One terminal of the operating coil for relay 431 is connected through sensing switch 401 to the positive bus 28. A holding circuit for the relay is provided through a pair of normally open contacts 451. The other terminal of the relay 'coil is connected to a common relay return line 452, the return circuit to the negative bus 29 being described in detail hereinafter.

In addition to contacts 451, relay 431 includes a pair of normally open contacts 453 and a pair of normally closed contacts 454. One side of contact pair 453 is connected to positive bus 28 and the other in this pair of contacts is connected to a capacitor 455 and to one side of normally closed contact pair 454. The remaining contact of pair 454 is connected to a resistor 456 utilized as a discharge resistor for capacitor 455. The resistor and capacitor are connected at a terminal 457 that is connected to one of a pair of normally closed contacts 458 in relay 432 to afford a series connection from capacitor 455 to an output circuit 459. Line 459 is connected to the second major unit 3303 of the control circuit.

One terminal of the operating coil for the second relay 432 is connected through sensing switch 402 to switch 401 in an arrangement that permits completion of a circuit connection to the positive bus 28 either through switch 401 or through contacts 451 of relay 431. A holding circuit is provided for relay 432 through a pair of normally open contacts 461 returned to bus 28. The other terminal of the operating coil for relay 432 is connected to line 452. Relay 432 further includes a pair of normally open contacts 463, one of which is connected to. positive bus 28 and the other of which is connected to a timing capacitor 465. Capacitor 465 is connected to a resistor 466 and to a pair of normally closed contacts 464 of relay 432 to provide a circuit arrangement similar to that for the initial timing capacitor 455. The common terminal 467 of capacitor 465 and resistor 466 is connected through a pair of normally closed contacts 468 in relay 433 to the output line 459.

The operating circuit for relay 433 is essentially a duplicate of that for circuit 432. Energization of the relay is eifected through closing of sensing switch 403 and is dependent upon prior completion of an operating circuit for relay 432. Again, relay 433 is provided with a suitable holding circuit. The output circuit for the relay, comprising a timing capacitor 475 and a discharge resistor 476, is connected to the next stage (not shown in the interconnecting and interlocking circuit unit 330A.

The penultimate connecting relay 440 in circuit 330A is generally similar to the preceding relays. The operating coil for relay 440 is connected to sensing switch 410 to provide an energizing circuit that is dependent upon prior completion of an energizing circuit in the preceding relay of the series. Relay 440 includes a pair of normally open contacts 481 that afford a holding circuit for the relay. In addition, relay 440 is provided with a pair of normally closed contacts 478 to provide a connection to line 459 for the timing capacitor in the preceding stage (not shown) of the interlocking relay circuit. As in the previous relay circuits, relay 440 includes a pair of normally open contacts 483, one of which is connected to bus 28 and the other of which is connected to a pair of normally closed contacts 484 and to a timing capacitor 485. A resistor 486 is connected in circuit with capacitor 485 with the normally closed contacts 484 interposed between the resistor and the capacitor. In this instance, the resistor and the capacitor are connected together at a terminal 487, which is connected directly to line 459 instead of being connected through a further stage in the sequence of interlocking relays.

Relay 441 has its operating coil connected through sensing switch 411 to an energizing circuit that, as before, is dependent upon energization of the preceding relay 440. Relay 441, however, does not have a holding circuit, the relay coil is returned directly to the negative bus 29. Relay 441 functions as a reset relay, the common return line 452 for all of the preceding relays being connected through a pair of normally closed contacts 491 in relay 441 and thence to the negative bus.

Output line 459 of circuit 330A is connected to one terminal of the operating coil of a start delay relay 501 n circuit 330B, the other terminal of the relay coil bemg returned to negative bus 29. Start delay relay 501 includes a first pair of normally open contacts 502 and a second pair of normally open contacts 503. One contact of pair 502 is connected directly to negative bus 29 and the other contact of this pair is connected through a resistor 504 to the emitter of a double-base unijunction transistor 505. A timing capacitor 510 is connected from 1; emitter of transistor 505 back to the negative bus One contact of pair 503 is connected directly to positive bus 28 and the other contact of this pair is connected to the collector of a conventional PNP switching transistor 506. The emitter of transistor 506 is connected through a resistor 507 to a first base electrode 508 of transistor 505. The base electrode of transistor 506, on the other hand, is connected to the first base electrode 509 of de- 'vice 505 through a parallel RC input circuit comprising a resistor 511 and a coupling capacitor 512. Base 509 is also returned to negative bus 29 through a load resistor 513. Finally, a variable resistance coupling circuit is pro- 13 vided between the emitters of devices 505 and 506, this circuit comprising a resistor 514 connected in series with a potentiometer 515 between the two emitter electrodes. A bypass capacitor 516 is connected from the emitter of triode 506 to bus 29.

The collector electrode of transistor 506 is connected to one terminal of the operating coil of a timing relay 521, the other terminal of the coil being returned to negative bus 29. Relay 521 is provided with a holding circuit through a pair of normally open contacts 522 that connect relay coil back to positive bus 28, the holding circuit including, in series, the emitter-collector circuit of transistor 506. A diode 523 is connected in parallel with the operating coil of relay 521.

Timing relay 521 further includes a pair of normally closed contacts 524 and a pair of normally open contacts 525. One of the normally closed contacts 524 is connected, by line 535, back to circuit 330A to a terminal 526 intermediate sensing switches 402 and 403. The other contact of pair 524 is connected to one terminal of the operating coil of a below-speed relay 527, the other terminal of the coil being connected to negative bus 29. The below-speed relay is provided with a holding circuit comprising the normally open contacts 528 of the relay, which atiord a connection back to terminal 526 in circuit 330A in parallel with the normally closed contacts 524 of relay 521. Relay 527 further includes a pair of normally closed contacts 529, one of which is also connected to terminal 526 in circuit 330A. The remaining contact of pair 529 in relay 527 is connected to one of the normally open contacts 525 in the timing relay 521. The other contact in pair 525 is connected to one terminal of the operating coil in an over-speed relay 531, the other terminal of the relay coil being returned to negative bus 29.

Over-speed relay 531 includes two sets of normally open contacts 532 and 533. A holding circuit for relay 531 when the relay is energized includes, in series, contacts 532 and contacts 525 of the timing relay 521. Contacts 533, on the other hand, are connected in series circuit relation with the operating coil of an actuator relay 534 between the positive and negative buses. Relay 534 may be considered a part of actuator 315 (see FIG. 4) and, in the discussion of operation provided hereinafter, it should be understood that energization of this relay is effective to actuate the retarder to braking condition.

When the retarder control system of FIGS. 4 and 5 is placed in operation, all of the relays thus far described are in unactuated or de-energized condition, the contacts for the relays being shown in this condition. If a railroad vehicle enters the retarder in the direction of the arrow A, the leading wheel on the car closes switch 401. This establishes an operating circuit for the coil relay 431, this circuit extending from bus 28 through switch 401 and the relay coil, through connector 452 and the normally closed contacts 491 of relay 441, to negative bus 29. As soon as relay 431 is actuated, contacts 451 are closed, establishing a holding circuit for the relay. Thus, relay 431 is energized and remains energized until reset by operation of relay 441 as described hereinafter.

Continued movement of a railroad vehicle into the retarder causes the leading wheel to engage and close switch 402. Closing of switch 402 completes an energizing circuit for relay 432. This circuit begins with bus 28 and eX- tends through the now-closed contacts 451 of relay 431, through switch 402 and the operating coil of relay 432, and through contacts 491 of relay 441 to the other bus 29. Again, actuation of the relay establishes a holding circuit through its contacts 461, which are closed as soon as the relay is energized. Consequently, subsequent opening of switch 402 due to continued movement of the railroad car does not cause relay 432 to drop out.

The continued movement of the railway vehicle into the retarder closes the switches in sequence and, in each instance, energizes the associated connector relay. In each 14 instance, the relay establishes its own holding circuit and remains energized.

When the leading wheel on the car closes switch 410, relay 440 is energized through circuit corresponding to those described hereinabove and including the holding circuit contacts of the preceding relay (not shown). Thus, insofar as the first section of the retarder is concerned, relay 440 operates in the same manner as the other relays ahead of it. Closing of switch 441, the last sensing swltch in the sequence in the first section of the retarder (see FIG. 4), energizes relay 441 through an operating circuit that includes the contacts 481 of relay 440, these contacts having been closed previously by actuation of relay 440. Energization of relay 441 opens contacts 491 and thereby opens the energizing circuit for each of relays 431 through 440. Relay 441 is not provided with a holding circuit and it is thus seen that actuation of this relay effectively deenergizes all of the preceding relays and resets circuit 330A for a subsequent speed-sensing operation.

It may happen that, at the time reset relay 441 is energized, another wheel of the same vehicle or a following vehicle may be at some intermediate point Wl'th respect to the first section of the retarder control system. That is, a wheel of the vehicle may be located at some point intermediate switches 401 and 411. The presence of this wheel in the first control section of the retarder, however, cannot initiate a speed sensing operation because actuation of each relay in the series 431-441 is dependent upon actuation of the preceding relay. Consequently, when relay 441 is energized and resets circuit 330A, the continued movement of a wheel through the system from a point intermediate switches 401 and 411 cannot start the speed sensing sequence and, accordingly, the vehicle wheel passes out of the system without triggering its operation. Of course, as soon as circuit 330A has been reset and switch 411 opens, the circuit is again ready for operation with respect to sensing of movement of the next wheel on the same or another vehicle entering the retarder control section and engaging switch 401.

The initial operating component of the speed sensing circuit 330B is relay 501, the start delay relay. Relay 501 is employed as a timing relay in the sense that it provides an initiating pulse signal of predetermined duration independent of the time interval during which the individual sensing switches may be closed. That is, relay 501 has a consistent operating time that is not dependent upon the time during which any of the switches are actuated or any of the relays 431441 remain energized. This consistent operating time is efiected by the connection for the operating coil of the relay relative to the capacitors 455, 465, 475, 485, and to the corresponding capacitors in the other unillustrated sections of circuit 330A.

Thus, when relay 431 is energized, contacts 453 are closed and contacts 454 are opened. The charging current of capacitor 455 becomes the energizing current for the operating coil of relay 501, since the capacitor is connected in a series circuit extending from positive bus 28 through contacts 453 and through the capacitor, through normally closed contacts 458 of relay 432, through output line 459 and the coil of the relay, to bus 29. Of course, the charging current for the capacitor 455 reduces rapidly, with the result that relay 501 is energized only for a brief period. The duration of this period is determined by the capacitance and internal resistance of capacitor 455. Resistor 456 does not aifect the charging time of the capacitor, since contacts 454 are opened when the capacitor is connected in circuit with the initial timing relay 501.

When the second connecting relay 432 is energized, contacts 458 are opened, disconnecting capacitor 455 from the operating circuit of relay 501. At the same time, however, contacts 463 close and contacts 464 open, establishing a new energizing circuit for timing relay 501 through capacitor 465. Again, it is the charging current for the capacitor that energizes relay 501, so that the relay is actuated only for a short predetermined interval dependent upon the impedance of the capacitor. It is thus seen that relay 501 is actuated each time one of the switches 401-410 is closed, but that the time interval during which the relay is actuated is not dependent upon the time the associated sensing switches close. Ultimately, when switch 411 is closed and reset relay 441 is energized the return of each of the relays 431-440 to its original de-energized condition affords a discharging circuit for the output capacitor of each of the relays. Thus, it may be seen that capacitor 455 is discharged through resistor 456, capacitor 465 discharges through resistor 466, and

so on.

The remaining circuits in timing unit 330B are utilized to time the intervals between operations of relay 501 in order to control operation of the retarder. That is, the pulse output signals from relay 501 constitute the basic timing signals employed to actuate the car retarder. The timing operation depends upon the charging time for capacitor 510, which, in turn, is controlled by and measured by the associated circuit of unit 330B. The illustrated circuit eliminates the high current requirements of more conventional time delay devices, such as a timing capacitor connected across a relay winding. Another attribute of the illustrated circuit is that it makes it possible to compensate for variations in the voltage across supply lines 28 and 29, eliminating any necessity for general power supply regulation.

Each time relay 501 is momentarily actuated, contacts 502 and 503 are both closed. Closing of contacts 503 completes an operating circuit from bus 28 through the contacts and through the operating coil of the main tirning relay 521 to bus 29. Thus, relay 521 is energized each time relay 501 is energized. Diode 523 does not affect actuation of relay 521, due to the polarity of its connection across the relay coil.

The closing of contacts 502, upon actuation of relay 501, discharges capacitor 510 through resistor 504 and the relay contacts. This reduces the emitter voltage of transistor 505, driving the transistor to cut-off. That is, transistor 505 is now non-conducting, providing very little current through the path including resistor 513 and base electrode 509. As noted above, relay 521 is energized, so that contacts 522 are closed. Hence, most of the supply volt-age appears across the operating winding of relay 521, due to the fact that transistor 506 is held in saturated condition as a result of the high base current provided for the transistor through resistors 511 and 513.

When relay 501 drops out, relay 521 is held in actuated condition. The opening of contacts 502 now permits charging of capacitor 510 through a circuit comprising bus 28, relay contacts 522, and the series resistors 514 and 555. It is this series RC circuit combination, comprising capacitor 510 and resistors 514 and 515, that performs the basic timing operation.

Transistor 505 can be compared, in its operation, to a thyratron. When the emitter voltage of the transistor rises to a value known as the peak point for the device, conduction is initiated. When conduction is established, in transistor 505, the emitter-base 509 resistance drops to a low value. Capacitor 510 is discharged through a path comprising base 509 and resistor 513, with most of the discharge current appearing across resistor 513. Consequently, when transistor 505 reaches conduction, a sharp pulse signal is developed across resistor 513 and is applied to the base of transistor 506 through capacitor 512, driving transistor 506 from saturation to cut-01f. The resultant change of device 506 from a very low impedance to a very high impedance, in its emitter-collector path, causes nearly the full supply volt-age to appear across the transistor, rather than across the operating coil of the main timing relay 521, so that the timing relay drops out.

When relay 521 drops out, the condition of the speed sensing circuit is restored to that which existed before relay 501 was operated. The timing interval during which relay 521 is held in actuated condition can be adjusted by adjustment of rheostat 515. Capacitor 516 and diode 523 are utilized to reduce the possibility of damage to transistors 505 and 506 that might be caused by transients resulting from operation of relay 521.

In the illustrated circuit arrangement, the effect of variations in the voltage supply upon timing is well compensated by the rise in the emitter peak voltage of device 505, required for firing the transistor, with the higher voltage across capacitor 510. Resistors 507 and 513 are selected, relative to the base resistances of bases 508 and 509, respectively, to compensate for changes in the emitter peak point firing voltage resulting from variations in temperature.

The main timing relay 521 controls operation of both the below-speed relay 527 and the above-speed relay 531. If a railroad vehicle wheel actuates sensing switch 402 after a time interval greater than the holding time of relay 521, the timing relay drops out, and an energizing circuit is established for below-speed relay 527. This circuit begins with bus 28 and extends through switch 402 (or through the parallel contacts 461 of relay 458 that are closed upon actuation of switch 402) through terminal 526 and the connecting circuit 535 to contacts 524 of relay 521. The circuit further extends from contacts 524 to the operating coil of relay 527 and then to the other bus 29. Consequently, the delayed closing of switch 402 causes thebelow-speed relay 527 to be actuated.

Energization of below-speed relay 527 closes contacts 528 to establish a holding circuit for the relay, which is maintained energized during the subsequent period in which a car traverses the initial section of track in the retarder. The operating circuit for relay 527 is interrupted only upon resetting of circuit 330A eifected in response to energization of relay 441 as described above. Acceleration of a car or other vehicle moving through the retarder is not detected by this particular operating circuit; however, this is not of critical importance because there are additional retarder sections that are independently operated as described hereinafter.

A car entering the retarder at a speed above the critical speed, however, actuates sensing switch 402 before the main timing relay 521 drops out. When this occurs, a circuit is established from bus 28 through switch 402 (or contacts 461) and terminal 526 to line 535, and then through the normally closed contacts 529 of relay 527 and contacts 525 of the main timing relay to the operating coil of over-speed relay 531, the other terminal of the coil being connected directly to bus 29. This operating circuit is effective to energize the above-speed relay 531, closing contacts 532 and 533. Relay 531 remains actuated through a holding circuit extending from the coil of the relay through contacts 525 and its own contacts 532 back to bus 28. The holding circuit is maintained as long as timing relay 521 remains actuated.

The main timing relay 521, on the other hand, remains continuously energized as long as the time required for the car passing through the retarder, between adjacent ones of switches 401-410, is less than the delay time of the relay as described above. If the braking effect in the first section of the retarder is sufficient to reduce the car speed to a point at which the time required to traverse the space between any two of the sensing switches exceeds the drop-out time of relay 521, the relay is, of course, released. If this should happen, contacts 525 open, de-energizing the over-speed relay 531. Moreover, contacts 524 close, completing the energizing circuit for the below-speed relay 527 as described before. Again, once the below-speed relay has been energized, it remains energized throughout the period of time in which the car moves through the first section of the retarder.

It is the above-speed relay 531 that actuates the retarder actuator 315 by energizing relay 534. That is, the retarder remains in its non-braking condition except when relay 531 is energized and is effective to actuate relay 534. It will be recognized that this speed control arrangement is based upon a single critical speed, but additional similar speed controls can be provided for a multilevel retarder in the same manner as in the previously described embodiments.

The second speed control 331 (FIG. 4) is essentially similar to speed control unit 336, and there is some overlapping of the sensing devices employed to control both. Thus, the first control element in the initial or interlocking circuit 331A of the second speed control (see FIG. 5) is a relay 440X. One terminal of the operating coil for relay 440X is connected to an additional pair of normally open contacts 540 in the penultimate relay 440 of circuit 330A. The other terminal of the relay coil is connected to a return line 552 corresponding to line 452 in circuit 330A. Thus, it is seen that relay 440X is energized upon actuation of relay 440 and that the closing of contacts 540 performs the same function, with respect to relay 440X, as the closing of the sensing switch 401 for the initial relay 431 in circuit 330A. Relay 440x is provided with its own holding circuit comprising its normally open contacts 541, which serve the same function as contacts 451 in the first section of the retarder control system. In addition, the relay is connected to a control capacitor 545 that performs the same timing function with respect to a start delay relay 551 in timing circuit 331B as is carried out by capacitor 455 in the previously described circuit.

The second connecting relay in circuit 331A, relay 441X, corresponds to the second relay 432 in the first section of the retarder control except that it does not have a separate sensing switch to provide for actuation. Instead, the coil of relay 441X is connected to a pair of normally open contacts 553 in the final relay 441 of the preceding section of the retarder control system. It can thus be seen that both of relays 44GX and 441X are actuated in overlapping relation to the final portion of the preceding section of the retarder, being controlled by sensing switches 410 and 411 through relays 440 and 441, respectively.

The third stage in circuit 331A comprises a relay 442 and the sensing switch 412. This relay has been shown in the drawing to make it clear that the succeeding stages in circuit 331A are the same as the remaining stages in circuit 330A. Moreover, it should be understood that the unillustrated portion of circuit 331B corresponds to the timing circuit 33033 in all respects, the ultimate output or control component of the circuit being the abovespeed relay 561, corresponding to relay 531 in the previously described arrangement.

The third and final control speed unit 332 of the system (FIG. 4) corresponds to the circuits of unit 339 described in detail in connection with FIG. 5. Again, there is an overlapping of two sensing switches between speed control units 331 and 332 to afford continuity of operation between the successive stages of the retarder.

Hence, while preferred embodiments of the invention have been described and illustrated, it is to be understood that they are capable of variation and modification and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claims.

We claim:

1. A speed-sensitive control system for a railway vehicle retarder comprising a traffic rail, retarder members, and operating means, actuatable between braking and released conditions, for operating said retarder members, comprising:

a series of sensing devices, located at predetermined spaced positions along the retarder trafiic rail, each sensing device being effective to develop an initiating signal pulse indicative of the presence of a railway vehicle Wheel at the sensing device position;

a slow-release timing relay for maintaining a predetermined energizing circuit for a predetermined time interval in response to an initiating signal;

means for effectively connecting said sensing devices, individually and in sequence, to said timing relay, as a vehicle traverses the retarder tratnc rail;

control means, connected to said energizing circuit and to said retarder operating means, for actuating said operating means to and maintaining said operating means in braking condition only so long as the timing relay continuously maintains said energizing circuit, following actuation of the first sensing device upon entrance of a first car wheel into said retarder;

and reset means, connected to the last sensing device, for resetting the control means and re-establishing .control thereof by the timing relay when the car wheel clears the last sensing device.

2. A speed-sensitive control system for a railway vehicle retarder comprising a trafiic rail, retarder members, and operating means, actuatable between braking and released conditions, for operating said retarder members, comprising:

a series of sensing devices, located at predetermined spaced positions along the retarder trafiic rail, each sensing device being efiective to develop an initiating pulse signal indicative of the presence of a railway vehicle wheel at the sensing device position;

signal-operated timing means, connected to said retarder operating means, for actuating said operating means to braking condition in response to applied initiating signals recurring within a predetermined critical maximum time interval;

and connecting means for effectively connecting said sensing devices, in sequence, to said timing means, as a vehicle traverses the retarder traffic rails, said connecting means comprising a series of control relays connected together for predetermined sequential operation by an interlocking circuit preventing application of an initiating signal to the timing means, from any sensing device, upon sensing of a different vehicle wheel than that starting the sequence.

3. A speed-sensitive control system for a railway vehicle retarder comprising a traflic rail, retarder members, and operating means, actuatable between a released condition and a plurality of dilferent braking conditions, for operating said retarder members, comprising:

a series of sensing devices, located at predetermined spaced positions along the retarder trafiic rail, each sensing device being eifective to develop an initiating pulse signal indicative of the presence of a railway vehicle wheel at the sensing device position;

signal-operated timing means, connected to said retarder operating means, for actuating said operating means to braking condition in response to said initiating signals, said timing means including a plurality of timing devices individually corresponding to the different braking conditions of said retarder operating means, said timing devices being connected for sequential operation to actuate the operating means to diiferent braking conditions in response to changes in the time intervals between initiating signals as a vehicle is slowed by the retarder;

and connecting means for effectively connecting said sensing devices, individually and in sequence, to the first timing device in said timing means, as a vehicle traverses the retarder trafiic rail, said connecting means comprising a series of electrically actuated switching devices connected together tEor predetermined sequential operation by an interlocking circuit preventing application of an initiating signal to the timing means, from any sensing device, upon sensing of a different vehicle wheel than that starting the sequence.

4. A speed-sensitive control system for a railway vehicle retarder comprising a trafiic rail, retarder members, and operating means, actuatable between a released condition and a plurality of difierent braking conditions, for operating said retarder members, comprising:

a series of sensing devices, located at predetermined spaced positions along the retarder traffic rail, each sensing device being effective to develop an initiating pulse signal indicative of the presence of a railway vehicle wheel at the sensing device position;

signal-operated timing means, said timing means including a plurality of slow-release timing relays individually corresponding to the different braking conditions of said retarder operating means, and each effective to establish an energizing circuit for a predetermined time interval in response .to an initiating signal, said timing relays being connected for sequential operation;

means for etfectively connecting said sensing devices, individually and in sequence, to the first timing relay in said timing means, as a vehicle traverses the retarder traflic rail;

control means, comprising a corresponding plurality of control relays individually connected to said energizing circuits and to said retarder operating means, for actuating said operating means to a selected braking condition related to the speed of a vehicle moving through the retarder;

and interlocking means for maintaining said operating means in a given braking condition only so long as the energizing circuit corresponding thereto is continuously maintained by the associated timing relay.

5. A speed-sensitive control system for a railway vehicle retarder comprising a trafiic rail, retarder members, and operating means, actuatable between braking and released conditions, for operating said retarder members, comprising:

sensing means comprising a series of momentary contact sensing device-s, located at predetermined regularly spaced positions along the retarder traflic rail, the spacing between devices being less than the minimum railway vehicle truck wheelbase and the total length of the sensing means being less than the truckto-truck spacing of a railway vehicle, each sensing device being effective to develop an initiating pulse signal indicative of the presence of a railway vehicle wheel at the sensing device position;

signal-operated timing means for establishing and maintaining an energizing circuit for a predetermined time interval in response to an initiating signal;

connecting means for etfectively connecting said sensing devices, individually and in sequence, to said timing means, as a vehicle traverses the retarder trafiic rail, said connecting means comprising a series of electrically actuated switching devices connected together for predetermined sequential operation by an interlocking circuit preventing application of an initiating signal to the timing means, from any sensing device, upon sensing of a different vehicle wheel than that starting the sequence;

and control means, connected to said energizing circuit and to said retarder operating means, for actuating said operating means to and maintaining said operating means in braking condition as long as the timing means continuously maintains said energizing circuit.

6. A speed-sensitive control system for a railway ve hicle retarder comprising a trafiic rail, retarder members, and operating means, actuatable between braking and released conditions, for operating said retarder members, comprising:

a series of sensing devices, located at predetermined spaced positions along the retarder traffic rail, each sensing device being efiective to develop an initiating pulse signal of brief but indefinite duration indicative of the movement of a railway vehicle wheel past the sensing device position;

a first timing device for converting applied initiating signals of varying duration to timing pulse signals of predetermined constant duration; means for effectively connecting said sensing devices individually and in sequence, to said first timing device as a vehicle traverses the retarder traflic rail;

a second timing device, coupled to said first timing device actuatable from an initial operating condition to a second condition in response to an applied pulse signal, said second timing device including means for maintaining the device in its second condition for a predetermined time interval representative of a critical vehicle speed; I i

and means connecting said second timing device to said retarder operating means to actuate said retarder to braking condition only so long as said second timing device is continuously maintained in its second condition by recurring pulse signals from said first timing device.

'7. A railway vehicle retarder control system according to claim 6, in which at least one of said timing devices comprises a relay connected in circuit with a timing capacitor and the time interval during which the relay remains actuated is determined by the charging time of the capacitor.

8. A speed-sensitive control system for a railway vehicle retarder comprising a trafiic rail, retarder members, and operating means, actuatable between braking and released conditions, for operating said retarder members, comprising:

a series of sensing devices, located at predetermined spaced positions along the retarder traffic rail, each sensing device being efiective to develop an initiating pulse signal indicative of the presence of a railway vehicle wheel at the sensing device position;

signal-operated timing means, including a main timing relay, actuatable from an initial condition to an actuated condition for a predetermined critical time interval in response to an applied signal;

connecting means for effectively connecting said sensing devices, individually and in sequence, to said timing means, as a vehicle traverses the retarder trafiic rail, said connecting means comprising a series of electrically actuated switching devices connected together for predetermined sequential operation by an interlocking circuit preventing application of an initiating signal to the timing means, from any sensing device, upon sensing of a difierent vehicle wheel than that starting the sequence;

an over-speed relay, connected to said retarder operating means, for actuating said operating means to braking condition in response :to actuation of the over-speed relay from an initial condition to an actuated condition;

and circuit means connecting said main timing relay to said over-speed relay to actuate said over-speed relay and maintain the same in actuated condition only so long as the main timing relay remains continuously actuated by initiating signals recurring in less than said critical time interval.

9. A railway vehicle retarder control system according to claim 8, in which said circuit means includes at belowspeed relay effective to prevent actuation of said overspeed relay at any time, during a given sequence of operation of said sensing devices, after said main timing relay has once reverted to its initial condition.

It). A speed-sensitive control system for a railway vehicle retarder comprising a trafiic rail, retarder members, and operating means, actuatable between braking and released conditions, for operating said retarder members, comprising:

a series of sensing devices, located at predetermined spaced positions along the retarder traffic rail, each sensing device being effective to develop an initiating pulse signal indicative of the presence of a railway vehicle wheel at the sensing device position;

21 22 signal-operated timing means, connected to said retarder initiating signal to the timing means, from any sensing Operating means, for tuating said operating means device, upon sensing of a different vehicle wheel to braking condition in response to applied initiating than that starting the sequence. signals recurring within a predetermined critical time interval, said timing means comprising a main timing 5 References Cited relay controlled in its hold-in time by charging of UNKTED STATES PATENTS a timing capacitor connected thereto, and further comprising a variable impedance connected to said gf' i t a1 timing capacitor to adjust the charging time of the 1958293 5/1934 Biggest :1 2461 82 capacitor; i and connecting means for efiectively connecting said 10 fiQ i %jg sensing devices, individually and in sequence, to said 2690238 9/1954 4 2 timing means, as a vehicle traverses the retarder 2819682 1/1958 2 1 23 5 g }g% traflic rail, said connecting means comprising a series of electrically actuated switching devices connected 15 Y I together for predetermined sequential operation by ARTHUR LA POINT P'lmary Examme" an interlocking circuit preventing application of an STANLEY KRAWCZEWICZ, Examiner- 

2. A SPEED-SENSITIVE CONTROL SYSTEM FOR A RAILWAY VEHICLE RETARDER COMPRISING A TRAFFIC RAIL, RETARDER MEMBERS, AND OPERATING MEANS, ACTUATABLE BETWEEN BRAKING AND RELEASED CONDITIONS, FOR OPERATING SAID RETARDER MEMBERS, COMPRISING: A SERIES OF SENSING DEVICES, LOCATED AT PREDETERMINED SPACED POSITIONS ALONG THE RETARDER TRAFFIC RAIL, EACH SENSING DEVICE BEING EFFECTIVE TO DEVELOP AN INITIATING PULSE SIGNAL INDICATIVE OF THE PRESENCE OF A RAILWAY VEHICLE WHEEL AT THE SENSING DEVICE POSITION; SIGNAL-OPERATED TIMING MEANS, CONNECTED TO SAID RETARDER OPERATING MEANS, FOR ACTUATING SAID OPERATING MEANS TO BRAKING CONDITION IN RESPONSE TO APPLIED INITIATING SIGNALS RECURRING WITHIN A PREDETERMINED CRITICAL MAXIMUM TIME INTERVAL; AND CONNECTING MEANS FOR EFFECTIVELY CONNECTING SAID SENSING DEVICES, IN SEQUENCE, TO SAID TIMINNG MEANS, AS A VEHICLE TRAVERSE THE RETARDER TRAFFIC RAILS, SAID CONNECTING MEANS COMPRISING A SERIES OF CONTROL RELAYS CONNECTED TOGETHER FOR PREDETERMINED SEQUENTIAL OPERATION BY AN INTERLOCKING CIRCUIT PREVENTING APPLICATION OF AN INITIATING SIGNAL TO THE TIMING MEANS, FROM ANY SENSING DEVICE, UPON SENSING OF A DIFFERENT VEHICLE WHEEL THAN THAT STARTING THE SEQUENCE. 